Jolt and Shake Issue

The jolting problem could be worn engine mounts or worn suspension parts. The shaking most commonly is an out-of-balance wheel but could also be caused by a bent wheel, broken tire belt, bent hub, even a warped brake rotor. Worn lower control arm bushings or struts could cause both problems. The best approach is to have the steering and suspension systems inspected at a tire and alignment shop.

For starters, watch the engine while a helper shifts between drive and reverse to see if it's rocking back and forth a lot. GM likes to use a "dog bone" mount on the top front. It isn't really a mount; it's to control engine movement. The rubber bushings in it can deteriorate. Idle speed that's too high can cause harsh engagement too.

Without knowing if other parts are related to the problem it's impossible to say if it will get worse. Instead, other parts could be damaged from the banging. In particular, exhaust parts are designed to shift position gradually as the engine rocks. If there's too much movement, that can stress those exhaust parts and hangers. Wire harnesses will be flexing a lot which leads to rubbed through wires and loose connector terminals. Fuel and emissions hoses will be flexing more than normal.

If engine movement appears to be normal, watch the two front wheels to see if they move when switching between forward and reverse. If one does, suspect the lower control arm bushings or strut. If idle speed is too high, suspect a vacuum leak. Use a spray bottle to spray water on the vacuum hoses and intake manifold gasket while the engine is still cold. If you see water get sucked in or the engine slows down momentarily, check that area for a leak. You can also pinch off vacuum hoses to try to identify one that's leaking.